Toothed belts to whose engaging surfaces a foundation fabric is adhesive-bonded for the purpose of protecting the surface are known from JP, U 62-204059 (U.S. Pat. No. 4,826,472; EP-B1 0 271 587) and other publications; however, in the foundation fabric thereof crimped yarns of synthetic fibers are used as weft yarns extending in the longitudinal direction of the toothed belt. These toothed belts are formed, as shown in FIG. 2, by locating a foundation fabric 2, tensil cords 3 and unvulcanized rubber 4 on a mold 1 having protrusions and recesses on its surface and by vulcanizing the unvulcanized rubber 4 by applying heat and pressure thereto; and, as shown in FIG. 3, the belt teeth 6 are formed on the engaging surface along the recesses of the mold 1. I.e., a requirement of said foundation fabric 2 is that it must be capable of being elongated during its formation by being subjected to low loads by as much as some ten percent from a predominantly flat condition to a condition in which it follows the protrusions and recesses of the mold 1. Accordingly, crimped yarns of synthetic fibers are used in this woven fabric 2 as weft yarns extending in the longitudinal direction of the toothed belt, so that the woven fabric can be easily elongated by stretching the crimps.
The foundation fabric of conventional toothed belts is woven in a 2/2 double-faced twill pattern, and false-twisted yarns of different false twist directions are combined in parallel and used as weft yarn so that the exposure condition of the yarns on both faces is equal.
Toothed belts require adequate durability because, being operated at high speeds while rotating on pulleys, repeated bending creates forces which may tear the foundation fabric off the engaging surface of the belt; there are even cases in which the foundation fabric has actually been torn off due to long use. Further, when the toothed belt is in operation, a momentum is transmitted by the engagement of the tooth profile of the toothed belt with the tooth profile of the pulleys; therefore, sounds are produced by the collision of the tooth surfaces when the tooth profiles engage, the friction between the tooth surfaces during rotation, the friction occurring when the toothed belt separates from the pulley, etc.; moreover, currents of air occur rapidly when the tooth profiles engage and disengage, producing a disagreeable noise.
These problems have hardly been addressed in the conventional toothed belts described above, which, lacking in durability, do not endure long periods of use, and which produce a fairly loud noise during operation.